This invention relates generally to turbine engines, and more specifically to methods and apparatus for operating turbine engines.
At least some known turbine engines include a plurality of rotor blades that extract rotational energy from fluid flow entering the turbine and a gas fuel cleanup system that heats the fluid entering the turbine. More specifically, at least some known gas fuel cleanup systems include a coalescing filter and a gas fuel superheater. The gas fuel heaters may heat fluid channeled to a plurality of gas turbines. However, during a plant outage, the temperature of the gas may approach the ambient air temperature if the gas pipe is routed above ground or may approach the ground temperature if routed below grade level. As a result, during a turbine restart, any gas fuel trapped between the heater and the gas turbine may not be at a sufficient operating temperature to prevent condensate formation.
To facilitate maintaining the operating temperature of the gas fuel, at least some known systems use an auxiliary startup coalescing filter and an auxiliary electric startup heater. However, installation of auxiliary startup filters and heaters may be costly and may be limited by space considerations. In addition, if an auxiliary startup filter and/or an auxiliary heater fail, the temperature of the working fluid may fall below the required superheat value that will prevent condensation during expansion through the gas control valves.
In one aspect, a method for operating a turbine is provided. The method includes supplying working fluid to a first flow path input and routing the fluid through a heating unit coupled in flow communication to the flow path between first flow path input and the turbine. The method also includes extracting a portion of the working fluid from first flow path at a point intermediate the heating unit and an inlet of the turbine. The method further includes re-circulating the extracted fluid through a second flow path such that the extracted fluid is discharged upstream from the heating unit.
In another aspect, a fluid delivery system for a turbine is provided. The fluid delivery system includes a first flow path for supplying working fluid to the turbine. The first flow path includes an input end and an output end, wherein the output end is coupled to the turbine. The fluid delivery system also includes a heating unit coupled in flow communication within the first flow path for heating the working fluid. The fluid delivery system further includes a second flow path comprising a first end and a second end. The first end is coupled in flow communication to the first flow path between the heating unit and the turbine for extracting a portion of the working fluid from the first flow path. The second end is coupled in flow communication to the first flow path between the first flow path input end and the heating unit such that a portion of the working fluid is re-circulated through the second flow path.
In a further aspect, a turbine is provided. The turbine includes an inlet, and a first flow path for supplying working fluid to the turbine. The first flow path includes an input end and an output end, wherein the output end is coupled to the turbine inlet. The turbine also includes a heating unit coupled between the first flow path input and output ends for heating the working fluid. The turbine further includes a second flow path including a first end and a second end, the second end flow path first end is coupled in flow communication to the first flow path between the heating unit and the turbine inlet for extracting a portion of the working fluid from the first flow path. The second flow path second end is coupled in flow communication with the second flow path between the first flow path inlet end and the heating unit.